This disclosure directs itself to a reversing configuration control for electric string instruments and a boost circuit usable therewith. The reversing configuration control permits switching between various combinations of a pair of pickup sensors, either widely separated or collocated in a common enclosure, in one of series or parallel with the pickup sensors being of like polarity, a single one of the pickup sensors, and in one of series or parallel with the pickup sensors being of opposite polarity, one with respect to the other. More in particular, the disclosure is directed to a reversing configuration control for string instruments that includes a pair of pickup sensors disposed on a string instrument in which voltages are output by the sensors responsive to vibration of at least one string of the string instrument and a multipole switch providing selective operative coupling of the pair of pickup sensors in various configurations to the output terminals is provided responsive to the position of displaceable contacts of the multipole switch. Still further, the system can provide selective operative coupling of the pair of pickup sensors in combination with the pickup sensors having like polarity, selection of a single one of the pair of pickup sensors, or can provide selective operative coupling of the pair of pickup sensors in combination with one of the pickup sensors having an opposite polarity with respect to the other pickup coil. Additionally, a reverse polarity boost circuit is provided to permit selective reduction of the effect of the reversed polarity pickup sensor and thereby boost the signal level output by the novel reversing configuration control circuits disclosed herein, as well as the signal level output by prior known reversing configuration control circuits.
Electric string instruments, such as electric guitars, electric bases, electric violins, etc., use at least one pickup sensor to convert the vibration of instrument's strings into electrical impulses. The sensors may be piezoelectric devices, optical sensors, microphones or the most commonly used type of pickup sensor; that of a magnetic pickup sensors. Magnetic pickup sensors are pickup coils that use the principle of direct electromagnetic induction. The signal generated by most pickup sensors are of insufficient strength to directly drive an audio transducer, such as a loudspeaker, so they must be amplified prior to being input to the audio transducer. While many of the pickup sensors either inherently include “built-in” preamplifiers or are available with preamplifiers incorporated therein, including magnetic pickup sensors, such “active” pickup sensors still require connection to an amplifier in order to drive most audio transducers.
Because of their natural inductive qualities, all magnetic pickups tend to pick up ambient electromagnetic interference (EMI) from electrical power wiring in the vicinity, such as the wiring in a building. The EMI from a 50 or 60 Hz power system can result in a noticeable “hum” in the amplified audio by from the audio transducer, particularly with poorly shielded single-sensor pickups. Double-sensor “Humbucker” pickups were invented as a way to overcoming the problem of unwanted ambient hum sounds. Humbucker pickups have two coils that are arranged with opposite magnetic poling and corresponding oppositely wound coils to produce a differential signal with respect to signals not generated as a result of the magnetic fields of the pickup. Since ambient electromagnetic noise affects both coils equally and since they are oppositely wound, the noise signals induced in the two sensors are canceled out. The two coils of a Humbucker are often wired in series to give a fuller and stronger sound. Humbucker type pickup sensors are now also available with dual active pickups where each pickup coil is coupled to its own dedicated preamplifier.
While most single sensor pickups in multiple pickup installations are wired in parallel with each other, it is also possible to wire them in series, producing a fuller and stronger sound. The two sensors of a Humbucker type pickup can also be connected in parallel. This results in a brighter sound, but at the cost of a lower output as with a single-sensor pickup, but with the pickup's hum-cancelling properties of the Humbucker still being retained. Using a multiple pole, multiple throw switch, such as a double pole, double throw switch (DPDT) or double pole three position switch, it is known in the art to switch the sensor configuration between series and parallel, and may also provide for a “sensor cut” configuration (a single sensor output), but use of such a switch to selectively provide a reverse polarity option has not heretofore been provided in the art.
By reversing the electrical polarity of one of two pickup sensors connected in series or parallel, whether in a Humbucker pickup or a configuration of two single pickup sensors, the concept of signal cancellation can be applied to the sound signals generated from the strings of the instrument. Signals from the two sensors of the same frequency will be cancelled to some degree as a function of the phase and amplitude differences between them. As the string movement adjacent the bridge is less than adjacent the neck of the instrument, the bridge pickup will necessarily generate higher frequencies, including harmonics, than that generated by a neck pickup. To a lesser degree, the same is true for the sensors of a Humbucker pickup. The sensor of a Humbucker pickup closest to the bridge of the instrument will generate higher frequencies than the sensor which is further from the bridge. Musicians have employed this concept to change the sound of their instrument to create particular effects. The reversing of the polarity of one sensor relative to the other substantially removes the lower fundamental frequencies in the output signal from the combined pickup sensors, leaving the higher frequencies and harmonics. To that end, sensor reversing switches have been added to prior art systems. Using a passive boost circuit to reduce the amplitude of the signals from the reversed polarity sensor reduces the subtractive effect and results in a stronger sound, but still with some muting of the lower frequencies. Either of the pickup sensors in the switched reversing configuration control disclosed herein may be reversed relative to the other, although it is usually the pickup sensor closest to the bridge that is reversed relative to the other pickup sensor by conventional pickup sensor reversing circuits.